An extension bar 1 includes a shank 2 and a square insert 6 projecting from the shank 2. A button 3 is put in the shank 2. A portion of the button 3 extends from the shank 2. A detent 4 is embedded in the square insert 6. A portion of the detent 4 extends from the square insert 6. A mechanism (not shown) is arranged between the button 3 and the detent 4 so that when the button 3 is pushed, the detent 4 is allowed to completely enter the square insert 6. Therefore, a user will have his or her fingers hurt by the button 3 if the extension bar 1 is accidentally rotated before the user takes his or her hand 5 off the extension bar 1.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in the prior art.